1. Field of the Invention
This invention relates to a levelling mechanism for use in maintaining a swather header level, particularly the header as used in a floating condition during the swathing operation.
2. Description of the Prior Art
There are marketed swathers which are of the self-propelled types, commonly termed "windrowers", and such machines include a tractor unit and a header. The tractor unit known as a windrower tractor is provided with a lift mechanism at the front, including a hydraulic system and linkage arrangement, for raising the header from a lowered operating position to a raised inoperative position free of the ground. Self-propelled windrowers of this type are manufactured and sold, for example, by Ford New Holland under the trade-mark SPEEDROWER, Models 2450 and 2550, and are specially designed for cutting, conditioning and windrowing hay. As the cutting of hay crops requires that the cut be made close to the ground, the header is provided with skid shoes which allow the hydraulic system to be actuated in a manner to move the header to the lowered operating position wherein the skid shoes ride on the ground and thus support the header with the cutting blade slightly above the ground level. As will be described in more detail below, the lift arrangement for such hay headers includes a pair of transversely spaced header lift assemblies, each including a single acting cylinder and a spring system for partially counteracting the weight of the header in the lowered position. When the cylinders, which are connected to a common hydraulic line, are actuated so that pressurized hydraulic fluid is provided from the line to cylinders, the header is raised. Because the header is carried by the transversely spaced skid shoes when cutting, levelling of the header is not a concern as the lift assemblies effectively operate independently. In fact, because the spaced skid shoes follow the ground contour, one end of the header can follow the ground to a higher level than the opposite end, and the hydraulic fluid simply flows from the cylinder which is being forced to a contracted condition to the other cylinder which is moving to a more extended condition.
Because a major cost of the windrower is in the windrower tractor unit, it is advantageous to be able to use the windrower tractor for other functions, including that of swathing grain crops. It is preferable, however, to utilize a different type of header for swathing grain, namely one which does not include conditioner rolls and which transfers the cut grain to a windrow opening of the header by a travelling belt rather than an auger feed. Also, because it is necessary to cut a grain crop at a greater distance from the ground, a grain swather does not ride on skid shoes but is held suspended at a higher elevation. With the above described lift assembly commonly provided on the hay windrower, such as the * SPEEDROWER and similar windrowers * - trade-mark sold by other agricultural equipment manufacturers, the grain crop swather can not be readily held in a level condition while swathing with the header held suspended above the ground because when the pair of hydraulic cylinders are not operated to their fully lifted positions, the fluid can be displaced from one lift cylinder to the other, depending on which end of the header is heavier.